As one of conventional mobile devices represented by mobile phones, PDA (Personal Digital Assistance) and the like, those mobile devices having a housing of a foldable type small in size, light in weight and excellent in protective function are widely used. The mobile device of this kind is difficult to manipulate the opening operation of the housing forming part of the mobile device as the housing becomes small in size. In the recent years, there has been proposed a mobile device which is excellent in the manipulation of the opening operation of the housing by providing the mobile device with an opening/closing device to ensure that the opening/closing operation of the mobile device is carried out simply by the pushing operation of the push button provided in the one hinged member of the housing of the mobile device.
As the opening/closing device of this kind, there has been widely known a mobile device (for example see following patent document 1) which comprises a plurality of rotation cams including a conversion cam for converting the pushing operation to the rotation motion when the pushing button is pushed, a release cam driven by the conversion cam and a returning spring, a fixed cam and a reversing cam to be operated by the release cam, the above cams being provided in a cylindrical guide member fixed to one hinged member to be hinged with the other hinged member. In response to the pushing operation of the pushing button, the engaging state between the rotation cam and the movable cam fixed to the housing and thus moved together with the housing is changed to make it possible for the opening/closing device to be opened and closed by using the urging force of the spring.    Patent document 1: Patent laying open publication 2003-232336